The use of aqueous polymer dispersions as binders in pigmented coating compositions is well known. For example, polyvinyl ester dispersions, including dispersions of polyvinyl acetate-ethylene-copolymers (hereinafter “VAE-copolymers”) are known binders for coating compositions. VAE-copolymers are prepared predominantly via emulsion polymerization and are used as aqueous VAE-copolymer dispersions. It is known that the glass transition temperature of these VAE-copolymers can be adjusted by varying the vinyl acetate to ethylene ratio of the copolymer, with higher amounts of ethylene units in the VAE-copolymer generally resulting in a decrease in glass transition temperature. In applications where non-tackyness is important, for example in paints or in renders or plasters, glass transition temperatures above 0° C. are strived for. VAE-copolymers in emulsions for paint and plaster or render applications in general possess ethylene contents of between 12 to 16% by weight. On the other hand, VAE-copolymers with high glass transition temperatures are often inferior as binders for coating compositions since these copolymers result in coating compositions with high minimum film forming temperatures (hereinafter “MFT”). A low MFT is essential in many coating applications. While the MFT can be lowered by adding cosolvents (coalsecing agents) to the formulation, the amount of such agents often should be kept low in view of ecological constraints. Therefore, development of a VAE-copolymer emulsion adapted ideally to a selected use is often a compromise between several variables.
VAE-copolymer emulsions have been used extensively for coating applications of different substrates, for example for carpet applications (see e.g. U.S. Pat. No. 6,359,076). This document discloses a crosslinkable carpet backing coating composition comprising an aqueous VAE-copolymer dispersion derived from 4 to 25% by weight of ethylene, 67 to 95% by weight of vinyl acetate and 0.1 to 8% by weight of an ethylenically unsaturated hydroxyfunctional monomer in combination with a selected crosslinking agent. No details about ethylene content and glass transition temperature of the VAE-dispersions used in the examples are disclosed.
U.S. Published Patent Application No. 2005/0287336 discloses VAE-copolymer emulsions adapted for carpet coating. The VAE-copolymer used in this application is comparatively soft and has a glass transition temperature between 0° C. and −40° C. These copolymers therefore have an ethylene content which is comparatively high, namely between 20 and 40 wt % of the total monomer content.
U.S. Pat. No. 7,064,091 discloses of a self-crosslinking polymer in a binder for non-wovens in order to improve the wet-strength of a wipe. As a binder, among others, VAE-copolymers are disclosed. These are derived from 50-95% by weight of a vinylester, by 5-30% by weight of ethylene as well as optionally by up to 12% by weight of a crosslinking monomer. These copolymer dispersions are comparatively soft, as the ethylene content of the specific copolymers in the examples is above 12% by weight.
U.S. Published Patent Application No. 2008/0044565 discloses a process for application of an adhesive comprising aqueous vinyl ester dispersion adhesive via a nozzle. Preferably vinylester-ethylene-copolymers are used, which are derived from 40-95% by weight of vinylesters, from up to 45% by weight of ethylene and from up to 60% by weight of other comonomers copolymerizable therewith.
U.S. Pat. No. 7,789,959 discloses a preservative-free coating agent comprising a selected vinylester-copolymer and a strong base for adjusting a pH-value above 10 in the dispersion. Copolymers derived from vinylacetate, ethylene and vinylesters of Versatic acids are disclosed. The ethylene content of these copolymers is typically between 10 and 20% by weight.
U.S. Pat. No. 5,143,966 discloses VAE-copolymer emulsions with improved wet adhesion, The copolymers are derived from 70-98% by weight of vinylacetate and 2-30% by weight of ethylene as well as from optionally up to 10% by weight of further monomers copolymerizable therewith. As stabilization system, a ternary mixture of polyvinylalcohols is used. This results in dispersions with relatively coarse particles with an average particle diameter of around 1 μm (dw).
U.S. Pat. No. 6,673,862 discloses a process for the preparation of VAE-copolymer emulsions stabilized with a mixture of polyethylene glycol and polyvinyl alcohol. The copolymers are derived from 50-95% by weight of vinylacetate and from 5-50% by weight of ethylene as well as optionally from up to 10% by weight of additional monomers copolymerizable therewith. In view of the stabilization system the average particle diameters of these dispersions are comparatively coarse and well above 500 nm (dw).
U.S. Pat. No. 4,267,090 discloses a process for the preparation of VAE-copolymer emulsions derived from 60-95% by weight of vinylacetate, from 5-40% by weight of ethylene and optionally from small amounts of additional monomers copolymerizable therewith. The polymerization reaction is carried out in the presence of a stabilization system consisting of an emulsifier and a protective colloid. Vinyl acetate monomer and emulsifier are added incrementally during the polymerization.
U.S. Pat. No. 4,108,819 discloses an aqueous VAE-copolymer dispersion comprising an epoxy component. The epoxy content is between 0.5 and 60% by weight of the total amount of monomers used during copolymerization. The content of vinyl acetate is between 60 and 95% by weight and the content of ethylene is between 5 and 40% by weight of the total amount of monomer. The emulsion polymerization can be carried out in the presence of emulsifiers and/or of protective colloids.
U.S. Pat. No. 5,180,772 discloses a dispersion comprising a VAE-copolymer with 60-94% by weight of vinylacetate units, 5-30% by weight of ethylene units and with 1-10% by weight of crosslinking units and comprising 1-45% by weight of tetramethylol glycoluril.
U.S. Pat. No. 6,624,243 discloses emulsions comprising copolymers, such as VAE-copolymer emulsions, functionalized with hydrolysable silane units and with epoxy-group containing units. These functionalized copolymers can be used in different paint formulations, e.g. in silicate-rich or in carbonate-rich formulations, and are said to provide an excellent wet-scrub resistance in both types of formulations. In the examples of this document, VAE-copolymers are disclosed with a content of ethylene units between 11 and 20% by weight.
We have now found that selected VAE-copolymer emulsions can provide coating compositions which are characterized by a balanced set of properties, such as low MFT combined with high scrub resistance and excellent blocking resistance of the resulting coatings. This combination of properties is comparable to those of commercially available acrylic paint formulations.